Flexible tanks

ABSTRACT

Flexible tanks for storage of fluids are constructed of interconnected panels of flexible material made of flexible woven and coated materials and with specific geometric panel configurations.

RELATED APPLICATIONS

This application is related to U.S. provisional application No. 61/865,375 filed Aug. 13, 2013.

FIELD OF THE INVENTION

Collapsible tanks for improved field performance related to stretch, storage, displacement and minimization of leakage and utilizing flexible, high-strength coated fabrics.

BACKGROUND

Traditionally, most tanks used for the field storage of liquid fuels, JP-8, water and other liquids are based on a “pillow tank” or similar designs. Such tanks are collapsible, flexible storage bladder tanks which provide temporary or longer term liquid storage. While these containers are designed for land based operations, they can also be utilized on the decks of vessels. These sizes ranging from 100 gallons to 210,000 gallons capacities and even larger custom tanks. Of course, with each design there are limitations to the tank and concerns regarding leakage. By considering material, fabrication techniques, fluid mechanic and design geometry variables, a number of unique tank designs were developed to overcome these issues. The present invention inherently reduces the stretch and hence the stress in the tank walls and welds, both at the design volume and at elevated temperatures. In addition, the present invention minimizes the number of weld seams, overall seam length or the need for certain weld types. These changes positively impact field life by reducing areas in the tank which serve as potential leak sources.

U.S. Pat. No. 7,213,970 and U.S. Pat. No. 7,503,885 both disclose flexible storage tanks with corners designed to improve resistance to leakage. Both patents cite the rounded corners as an improvement on pressure, yet both contain a significant number of panels and even directly cite a plurality of panels in their claims.

U.S. Pat. No. 4,865,096 also discloses a tank design but again suffers from less than preferred weld placements. The present invention seeks to minimize the number of panels in the tank and minimize the use of welds and weld seams.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing depicting the effect of liquid pressure on a standard design.

FIG. 2 is a drawing detailing fill versus warp characteristics.

FIG. 3 illustrates a standard pillow tank design.

FIG. 4A illustrates of a Canoe End tank of the present disclosure.

FIG. 4B illustrates panels of the canoe end tank of FIG. 4A.

FIG. 5A illustrates a multi panel trapezoidal tank of the present disclosure.

FIG. 5B illustrates panels of the tank of FIG. 5A.

FIG. 6A illustrates a Dogbone Trapezoid tank of the present disclosure.

FIG. 6B illustrates panels of the tank of FIG. 6A.

FIG. 7A illustrates a Quonset Hut tank of the present disclosure.

FIG. 7B illustrates panels of the tank of FIG. 7A.

DETAILED DESCRIPTION

In one embodiment the present invention discloses a flexible canoe ends design storage tank comprising two or more panels, each panel bonded by seams with others of the panels to enclose a storage volume, a left side pocket formed by one or more panels, a right side pocket formed by one or more panels, an optional middle section formed by one or more panels and the left side pocket, right side pocket and optional middle sections being assembled in a manner to maximize the tank base and maintain a low fill height with low stretch.

In another embodiment the present invention discloses a flexible multi panel trapezoidal design storage tank comprising, four or more panels, each panel bonded by seams with others of the panels to enclose a storage volume, a large rectangular panel formed by one or more panels, a small rectangular panel formed by one or more panels, two or more side panels, and the large rectangle, small rectangle and two or more side panels being assembled in a manner to maximize the base corners contact with the surface below and have low stretch on the small rectangle.

In yet another embodiment the present invention discloses a flexible dogbone trapezoid design storage tank comprising two or more panels, each panel bonded by seams with others of the panels to enclose a storage volume, a top rounded-corner square formed by one or more panels, a bottom envelope formed by one or more panels, and the top rounded-corner square and the bottom envelope being assembled in a manner to maximize the base corners contact with the surface below and have low stretch on the top rounded-corner square.

In still yet another embodiment the present invention discloses a flexible quonset but design storage tank comprising three or more panels, each panel bonded by seams with others of the panels to enclose a storage volume, an oval shaped left end-piece formed by one or more panels, an oval shaped right end-piece formed by one or more panels, a tube piece formed by one or more panels, and the oval shaped left end-piece, the oval shaped right end-piece and the tube piece being assembled in a manner to create a tank with a rectangular footprint with a taller height.

The present invention utilizes designs to reduce the total number of “T” seams and the total seam length. Furthermore, the present invention creates designs which keeps the tank bottom on the ground, thereby reducing peripheral (“edge”) hydrostatic effects on the tanks top and welds. This is accomplished by utilizing new geometrical designs. These designs may add 5-15% more material over traditional “pillow” tank designs, but this further reduces tank stress at target volumes. These new geometries aid in offsetting the difference between warp and fill directional stretch characteristics of material. In addition, closing seams are located on the bottom of the tank where hydrostatic pressure minimizes material stretch.

FIG. 1 illustrates the effect of hydro-static pressure on tank stretch for a typical prior art pillow tank T. As the tank T fills, the center of the tank rises quicker than the edges, this is due to the tanks fabrication and geometry. When the tank reaches 50-75% of its target volume, the edges begin to lift from the ground. As the tank is filled to its target volume or over-filled, the fluid pushes down on the elevated wings 1 due to hydro-static pressure. Pressure throughout the tank is equal in accordance with Pascal's Principle. In turn, this creates greater stretch on the top and middle zones 2 of the tank.

FIG. 2 illustrates the directionality of a coated fabric tank panel P made of coated woven material of the type manufactured by various manufacturers including Seaman Corporation, The narrow or fill direction F typically stretching two to three times more than the long or warp direction W, when using a material similar to Seaman Corporation 1940 PTFF MS 337 coated fabric.

FIG. 3 details a standard (prior art) Pillow Tank PT with elevated corners C and ends E. In this example there are 6 panels welded to one another first, overlapping along the warp (long) direction of the material. After the panels are welded to form a rectangular blanket, the remaining two warp ends of the blanket are welded to each other to form a tube. Both ends of the tube are then welded independently with closing seams to complete the Pillow Tank. The welds located along the warp seams are typically shingle, alternate overlap or double butt seam welds. The closing seams are typically a bottom flap over top shear seam, a fold over prayer weld or a double butt seam. Other types of seams used are lapped, double butted, shingle type or alternating. Material ring, oval doublers or oval triplers are added in the panels where the vent, filler-discharge manway and/or drain are located for additional support around the cast fittings and fasteners.

FIG. 4A illustrates a Canoe End tank CE of the present disclosure. The canoe end tank has “canoe” shaped panels which form the end closing seams. As further illustrated in FIG. 4B, for each end 41, 42 (E1, E2) two canoe shapes, 41 and 42, and 43 and 44, are welded to each other with a simple overlap weld, forming a pocket. The two canoe pockets are then joined to one another by an overlap or double butt seam welding the center panel CP 45 along both sides of its warp edge. Other types of seams used are lapped, double butted, shingle type or alternating. A final closing seam is created between the ends of the center panel(s) on the bottom of the tank. The volumetric size of the canoe end tank CE is flexible in that it can be easily scaled to larger tank sizes. This is done by increasing the length of the long axis of the canoe ends E1, E2 and adding multiple longer, additional, continuous center panels which have been welded to form a blanket. Even in a 50% overfill condition (e.g. 4500 gallons) as shown in FIG. 4A, the majority of this tank base remains on the ground in comparison to the pillow tank shown in FIG. 3. The canoe end tank CE also exhibits the lowest fill height at maximum over-fill of all tanks of the present invention and the lowest stretch. Most notably there are only 6 “T” seams on this tank which are the result of there being only 5 panels. These T seams occur where the canoe ends join to the center panel and the ends of the closing seam where it meets the canoe ends on the bottom.

FIGS. 5A and 5B depict a Multi Panel Trapezoid tank (MPT) of the present disclosure, and FIGS. 6A and 6B depict a Dogbone Trapezoid tank (DTT) of the present disclosure. The corners of the MPT and OTT designs remain on the ground in a partially or fully filled state, and even in a 50% overfill state as shown for example in the 4500 gallons embodiment shown in FIG. 5A. The MPT is formed by three top panels welded together, 3 bottom panels and 4 trapezoidal side panels. When filled, the resultant shape is a truncated, square frustum. While the MPT design increases the number of welds necessary, this is offset by the lower stretch measured on its top panels when compared to the prior art pillow tank designs. In addition, the side trapezoidal panels do not see increased stress translated from the top of the tank.

In the DTT design the panels which form the top have an angled edge which interfaces with the sides. The panel geometry balances warp versus fill stretch differences by offsetting the top and bottom assemblies by 90° as illustrated in FIG. 6B. The panel assembly of the DTT requires only 8 welds as compared to 10 separate panels with 20 distinct weld seams in the MPT. One embodiment includes adding the outer Dogbone shaped top end to the bottom blanket first, and then closing same by adding the top center panel, is much more efficient fabrication. Also, this design can be readily scaled to much larger tank sizes by increasing the length of the panels. As with the Multi Panel Trapezoid design the Dogbone Trapezoid exhibits lower stretch as measured on its top panels and side panels. As illustrated in FIG. 6A, the corners of the tank remain on the ground, even in a 50% overfill state as shown (approx. 4500 gallons).

FIGS. 7A and 7B illustrate an alternate embodiment of a flexible tank of the present disclosure, referred to in general as a Quonset Hut tank QHT. The QHT in a filled or partially filled state results in a taller tank than other embodiments and has a generally rectangular footprint. This is due to the liberal radius on the kidney shaped end panels which allow for easier welding without material puckering. The QHT can be scaled provided the end panels have a 2 to 3 foot minimal radius and the height of the panel does not exceed the fill width of currently available material. To keep the QHT from bowing out on these ends, the center panels 73, 74, 75 form an hour glass shape that help to pull the ends 71, 72 in at the top. There is one central closing seam across the bottom of the tank, running from one end panel to the other end panel.

In preferred embodiments, any of the disclosed tanks can be made of 2819 (30 gallon water prototype evaluation tanks) or 1940 PTFF MS 337 (field test tanks). In side by side field studies with JP-8, the flexible tanks of the present disclosure have been found to have fewer and less severe leaks than prior art tanks. Any of the flexible tanks of the present disclosure can utilize lapped, shingle type, alternating, bottom flap over top shear, fold over prayer weld or double butt seams. 

What is claimed is:
 1. A flexible tank comprising: A plurality of interconnected panels, each panel bonded to adjoining panels to define a tank cavity; a left side pocket formed by one or more panels; a right side pocket formed by one or more panels; an middle section formed by one or more panels; and the left side pocket, right side pocket and optional middle sections being assembled in a manner to maximize the tank base and maintain a low fill height with low stretch of the panels.
 2. The tank of claim 1 further comprising: five panels where four of the panels are rectangular and have two rounded adjacent corners, two of the four panels are bonded to form the left side pocket and two of the four panels are bonded to form the right side pocket; and one of the four panels is the middle section which is a rectangle and is bonded to the left side pocket and the right side pocket and to itself.
 3. A flexible multi panel trapezoidal design storage tank comprising: four or more panels, each panel bonded by seams with others of the panels to enclose a storage volume; a large rectangular panel formed by one or more panels; a small rectangular panel formed by one or more panels; two or more side panels; and the large rectangle, small rectangle and two or more side panels being assembled in a manner to maximize the base corners contact with the surface below and have low stretch on the small rectangle.
 4. The multi panel trapezoidal design storage tank of claim 3 further comprising: ten panels where four of the panels are side panel trapezoids and six of the panels are rectangles; and three of the rectangle panels are bonded to one another to form the large rectangle, three of the rectangle panels are bonded to one another to form the small rectangle, the long parallel edges of the side trapezoids bonded to the larger rectangle and the short parallel edges of the side trapezoids bonded to the small rectangle and the non-parallel edges of the side trapezoids bonded to one another. 